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Two Charts: Not One
Summary: [This abstract is based on the authors' abstract.]Because data coming from a typical operating process do not vary about a fixed mean, the operation of traditional control charts may be inconsistent. It is shown that a nonstationary model provides a continuously updated local mean level that can be used to produce both a bounded adjustment chart for determining when to adjust the process to achieve maximum economy and a Shewhart monitoring chart identifying assignable causes of trouble applied to the deviations from the local mean. Estimation of the mean and standard deviation are not required.
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- Topics: Statistical Process Control (SPC), Statistics, Engineering
- Keywords: Exponentially weighted moving average control charts (EWMA), ARIMA time series models, Monitoring, Noise, Design of control charts, Shewhart control chart, Stationary process
- Author: Box, George E. P.; Paniagua-Quinones
- Journal: Quality Engineering